Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.

User Name:

Password

Please enter a password for your user account. Note that passwords are case-sensitive.

Password:

Confirm Password:

Email Address

Please enter a valid email address for yourself.

Email Address:

Log-in

User Name

Remember Me?

Password

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options

Miscellaneous Options

Automatically parse links in text

Automatically embed media (requires automatic parsing of links in text to be on).

Automatically retrieve titles from external links

Topic Review (Newest First)

01-20-2013 11:29 AM

cobalt327

Quote:

Originally Posted by jdaviscgaz

One ? Off subject why did this post move? Couldn't find a carb specific site. Just not sure where I screwed up for future use.

You didn't screw up, it apparently just wasn't technical enough for the Engine forum.

01-20-2013 07:43 AM

jdaviscgaz

I got it thanks to you guys

Pulled the carb apart and noticed that the accel pump was sitting pretty far down in the cylinder so removed that one and placed a shorter one from another Quadra jet honed the cylinder with dremal sanding tube (just enough to scuff the edges to break the glaze)replaced check ball. Started it up and it wouldn't fire. After some cursing and tears haha just kidding on tears. Found I was out of gas. Put a couple of gallons in it and varoom she's alive and singing. Grab a turkey and set it over the back wheels were gunna smoke it. Thank you guys for the help your awesome. One ? Off subject why did this post move? Couldn't find a carb specific site. Just not sure where I screwed up for future use.

01-14-2013 09:50 PM

cobalt327

You're quite welcome. There is a guy, "Lars" who has also posted extensively on the Q-jet. He knows his stuff. Below is one of his posts (there are other pages by him if you do a search).

Plugged accelerator pump transfer holes in air horn
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: There is a tiny transfer hole that runs horizontally in the air horn, just inside of the actual accelerator pump discharge orifice. It is common for this to be plugged with some type of debris, especially in carbs that have been sitting around for a while. If this passage is plugged, there will not be any accelerator pump shot.

Jammed accelerator pump check ball
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: This is a common problem in carbs that have been allowed to “dry out” for a while. Sediment in the bottom of the fuel bowl will lock up the check ball as if it were set in concrete. This will prevent any accelerator pump discharge.

Accelerator Pump Rod Installed in Wrong Hole in Pump Arm
Results in: Off-idle stumble or hesitation.
Comments: There are two holes in the accelerator pump lever arm for the lever arm rod to engage into: Inner and Outer. The outer hole produces a leaner pump shot, and can cause a lean stumble on engines requiring a robust pump shot. Corvettes and performance cars always used the rich, inner pump arm hole.

Jammed accelerator pump
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: This is becoming a common problem. The alcohol additives in modern fuels are not compatible with the materials used in many accelerator pumps (even some of the pumps in brand new carb kits). This causes the pump plungers to swell up and to seize in the pump bore. The spring on the pump shaft still allows the shaft to move up and down, making it look as if the pump is functioning. But the pump itself can be seized up solid in the bore with the shaft working just fine. To fix this, you must install a pump that is specifically compatible with alcohol.

Worn accelerator pump
Results in: Off-idle stumble or hesitation, hard cold-start.
Comments: Common on older carbs and on carbs that have been allowed to dry out (vehicles stored without being started through the entire winter season). The rubber plunger material will dry out and shrivel up, making the accelerator pump completely ineffective. The pump must be replaced.

01-14-2013 05:23 PM

jdaviscgaz

Yeah duh. Sorry about that yes the it is for sure the accelerator pump that is malfunctioning I did move the linkage in and that's where I got the little squirt at WOT, but on outside nothing acts as if it's dry.will try these fixes you suggest. Thanks

01-14-2013 04:05 PM

cobalt327

Quote:

Originally Posted by jdaviscgaz

Certain of the metering rods and jets to be lined up. Noticing that the power piston has to be pushed at WOT before the gas is purged up to the exit site just above the venturi. Thinking that since the cylinder that the power piston is in is a tapered cylinder that I have the wrong plunger seat, and it is not sealing to push until the bottom of the cylinder. On the other models I've tried slightest movement of throttle actuated this part of the carb easily. The one I took out matched the one I put in but then again it didn't work either. Or fuel is just not getting to the power piston site which would have to be float level problems

Actually the part you're talking about is the accelerator pump. The power piston is controlled by vacuum and its job is to position the metering rods in the jets at the right level.

If the accelerator pump isn't working correctly, start by attaching the linkage to the hole nearest the pivot. That will give the biggest shot of fuel.

There are several different lengths of the rod the accelerator pump uses, if it's the wrong length this can have a bad effect.

If the springs are mixed up and the one for the filter is used on the accelerator pump, or the return spring is swapped w/the override spring on the shaft for instance, that can cause it to work poorly. If the piston seal is wrong it can have a hard time pushing fuel and/or allowing the pump to refill.

There's a ball that acts as a check valve under a screw in the float bowl, driver side. Be sure the ball is in place and sealing as it should. The check ball seat can be re-formed by carefully tapping an old check ball against the seat using a small punch and light mallet/hammer.

Sometimes the accelerator pump bore gets glazed where it doesn't seal against the piston very well. The bore can be lightly honed using 600 grit wet or dry and WD-40 or a similar solvent. I use a wooden dowel w/a piece of cloth wrapped around the dowel and the emery paper wrapped around the cloth. Then make like a boy scout starting a fire or like you're lapping a valve. You don't want to remove the finish, just break the glaze ever so lightly and to smooth the bore.

01-14-2013 01:22 PM

jdaviscgaz

q-jet power piston

Certain of the metering rods and jets to be lined up. Noticing that the power piston has to be pushed at WOT before the gas is purged up to the exit site just above the venturi. Thinking that since the cylinder that the power piston is in is a tapered cylinder that I have the wrong plunger seat, and it is not sealing to push until the bottom of the cylinder. On the other models I've tried slightest movement of throttle actuated this part of the carb easily. The one I took out matched the one I put in but then again it didn't work either. Or fuel is just not getting to the power piston site which would have to be float level problems

01-13-2013 08:44 PM

cal1320

Take carb cleaner and spray lightly into carb when it starts to die. If it continues to run one spray, it is too lean. If the spray kills the engine, it's too rich. If too lean, late 70's early 80's q jets sometimes need 6-8 turns out on the mixture screws. Read up on q jet power pistons. Make sure you have the primary rods inserted properly into the jets and the pp can move freely.

01-13-2013 03:08 PM

jdaviscgaz

found the problem

Carbuetor is the issue stiil not sure of the exact location of the problem but i found another quadra jet carb that worked previously and got a nice idle out of it the accel pump is being a little stubborn but in time is starting to respond. problem soved but not at the finish line yet .

quick breakdown of events.
swapped out a 305 with qjet and hei
replaced qjet with holley mani and edelbrock carb and mechanical dist over fueling issuse sooty pluygs
switched back to qjet and mani still problems with idle even after 5 rebuild attemps switched out mechanical dist to hei and replaced qjet with diffent one idle and rough running gone.

thinking the plugs on carb were leaking even after epoxy attemp.

my best advice is to not let your children in your work space to adjust all the screws on your cab while its off your motor. or this may help to reduce troubleshooting time frame.

i think im going to start with the hei. i have the original one just wire it back up the way it was and start there. my buddy mentioned something about it being dialed really far advance to make it run cause its an HEI but not hooked up to a ecm. is this right. now im thinking that if it truly has some kind of radical cam in it do you have to advance the timing to make the motor run. when told the specs to time it i was told 8 deg., but im hearing you mention 36 deg., and my buddy say something about 40deg. when it was running. i thought he was just talking crap. i wondering if theres a hidden message here.

any thoughts? sometimes i think to hard and skip the obvious.

01-10-2013 01:51 PM

techinspector1

Quote:

Originally Posted by jdaviscgaz

any ideas?

First thing I thought when I read your post was excessive fuel pressure. Quads won't tolerate much more than 5 psi at the needle and seat. More pressure than that will overpower the needle and blow raw fuel into the intake manifold, creating the nightmare you describe.

Tee off at the carb inlet and run a small pressure line (copper/nylon) back to the firewall, up past the hood lip and onto the cowl in front of the windshield. On the cowl, mount a mechanical 0-15 psi fuel pressure gauge so that you can monitor it through the windshield as you drive. Never-Never-Never run a live fuel pressure line into the driver's compartment. If you want to mount the gauge and leave it there, figure up a nice mount and some way to cover it against rain (I might be thinkin' a modified clear Tupperware bowl). If you just want to get your problem under control and then remove the gauge, mount it to the cowl with tie-wraps, duct tape or whatever.

If you're using an electric fuel pump, then you may need to mount and plumb an adjustable fuel pressure regulator into the system. If you are using a mechanical fuel pump, regulators don't work really well with them, so use a different pump that produces less pressure, maybe something like this....Carter Muscle Car Mechanical Fuel Pumps GM4685 - SummitRacing.com

The other thing that will help if the motor is cammed-up, is dialing in more initial spark advance at the crank. You will need ~36 degrees total timing, which is the sum of initial and centrifugal. Depending on the cam, the motor will want more at the crank and less at the weights, again, for a total max of ~36. You might get a kit and try different combinations of advance at the weights and at the crank. In other words, you might try 16 at the crank and 20 in the weights, for a total of 36. Again, since you don't know the cam specs, you will have to experiment. 12 and 24 might work best. You just have to play with it and find the best results for your combination.

Actually, I'd begin the experimentation with an HEI. They're cheap to buy new or you could buy one out of a boneyard and clean it up. Run a new, dedicated electrical wire from the starter switch to the + on the HEI. Do not use any wires that are already on the truck to supply current to the dizzy. USE A NEW LINE, 10 gauge. Bulletproof. Let me say this again with emphasis....DO NOT USE ANY WIRES THAT ARE ALREADY ON THE TRUCK TO SUPPLY CURRENT TO THE DIZZY!!!!!!
Here's a simple, cheap kit to begin with....Summit Racing® HEI Advance Curve Kits SUM-G5212 - SummitRacing.com
Use this kit from Crane to dial in your vacuum advance.....Crane Vacuum Advance Kits 99600-1 - SummitRacing.com

Oftentimes, we find that the inertia ring on the damper has rotated circumferentially in relation the the hub of the damper. When this happens, you can no longer time the motor with a timing light because the ring does not coincide with the piston being at top dead center. Read through this turorial and fix the problem if you suspect that the ring has slipped on your damper.http://www.crankshaftcoalition.com/w...op_dead_center

01-10-2013 12:42 PM

jdaviscgaz

searching for an idle problem fix

im almost done swapping v8 into s10. 1983 305 been told a different cam in it, not sure though, quadra jet carb 1980 and manifold, turbo 350. this motor an tranny where in another s10 fired, ran, idled, even drove it onto a trailer so it has worked 3months ago. now back together and cant get this thing to idle. i think its over fueling but no smoke from exhuat. the different item from 3 months ago til now is distributer. it had an hei dist with the weights robbed off of it and no vac pod so replaced it with what i want to call a regular dist in fear of calling it something its not, external coil, points, vac pod, just plan stock v8 distributor.

list of things ive tried

epoxy plugs on qjet
vac leaks with carb cleaner
rebuild kit
had this carb apart 4 times now not dirty

things that look suspicious

the points seem to be generating with dust on them. am i burning them up?

start the truck and bring the rpms up to 2000-2500 ?? no tack runs with very minor hicups but all and all smooth let off of the gas and let it idle and it starts running rough and dies. back to the starter button and cranks for 5-7 seconds and fires rpms are high (no throttle) for 5-10 seconds and idles downs runs rough and dies.